Intro

This is a simple sketch demonstrating the capability of the TTGO T-Beam as a TTN Mapper Node on The Things Network LoraWAN.

Derived from sbiermann/Lora-TTNMapper-ESP32 and with some information/inspiration from cyberman54/ESP32-Paxcounter and Edzelf/LoRa.

Software dependencies

Arduino IDE ESP32 extension

TinyGPS++

LMIC-Arduino : Make sure to get the last version - 1.5.0+arduino-2 currently - because the arduino IDE library updater is getting confused by the versioning scheme of that library. If you are on a 915 Mhz - ie USA - network you must modify the lmic library "config.h" file accordingly !

Instructions

Only on the oldest versions of the board you need to connect the T-Beam DIO1 pin marked Lora1 to the pin 33 - So that the ESP32 can read that output from the Lora module. Optionally you can also connect the Lora2 output to GPIO 32, but this is not needed here.

You can program the T-Beam using the Arduino ESP32 board 'T-Beam'.

On The Things Network side, the settings needed are available here.

Configure the Payload decoder for TTNv2 with:

function Decoder(bytes, port) {
    var decoded = {};

    decoded.latitude = ((bytes[0]<<16)>>>0) + ((bytes[1]<<8)>>>0) + bytes[2];
    decoded.latitude = (decoded.latitude / 16777215.0 * 180) - 90;

    decoded.longitude = ((bytes[3]<<16)>>>0) + ((bytes[4]<<8)>>>0) + bytes[5];
    decoded.longitude = (decoded.longitude / 16777215.0 * 360) - 180;

    var altValue = ((bytes[6]<<8)>>>0) + bytes[7];
    var sign = bytes[6] & (1 << 7);
    if(sign)
    {
        decoded.altitude = 0xFFFF0000 | altValue;
    }
    else
    {
        decoded.altitude = altValue;
    }

    decoded.hdop = bytes[8] / 10.0;

    return decoded;
}

For TTNv3 you can use the following function:

function decodeUplink(input) {
    var decoded = {};

    decoded.latitude = ((input.bytes[0]<<16)>>>0) + ((input.bytes[1]<<8)>>>0) + input.bytes[2];
    decoded.latitude = (decoded.latitude / 16777215.0 * 180) - 90;

    decoded.longitude = ((input.bytes[3]<<16)>>>0) + ((input.bytes[4]<<8)>>>0) + input.bytes[5];
    decoded.longitude = (decoded.longitude / 16777215.0 * 360) - 180;

    var altValue = ((input.bytes[6]<<8)>>>0) + input.bytes[7];
    var sign = input.bytes[6] & (1 << 7);
    if(sign)
    {
        decoded.altitude = 0xFFFF0000 | altValue;
    }
    else
    {
        decoded.altitude = altValue;
    }

    decoded.hdop = input.bytes[8] / 10.0;

    return { 
      data: decoded
    }
}

Let me know if more detailed instructions are needed.

Todolist

• Switch to the maintained version of the arduino-lmic library.
• Manage and document the different T-Beam revisions/versions.
• Save and reload the frame counter somewhere - GPS RTC data ? SPIFFS ? EEPROM ? - so I can check the "Frame Counter Checks" box as recommended on TTN. <== counter is stored in slow RTC memory so it's kept after deep sleep, thanks to @christianwicke - Still investigating the GPS module Battery Backed RAM for saving after power off.
• Also save the GPS 'status' so that on next boot it gets a fix faster.
• Adapt the data send frequency based on current velocity : When not moving, an update per hour should be enough.

Let me know if you think anything else would make sense for a TTN mapper node : Open an issue, I will consider it.